Exhaust and gas recirculating system

ABSTRACT

An exhaust gas recirculation system is disclosed employing a primary control valve having a vacuum operated servo mechanism for controlling the admission of recirculating gases. The servo mechanism is operated in response to a modulated vacuum signal derived principally from intake manifold vacuum. Modulation of the vacuum signal is achieved by three control means connected in series, one of which functions in response to a differential between carbureted venturi vacuum and the intake manifold vacuum, another control means operates to prevent communication of the vacuum signal to the servo mechanism during prolonged steady or nearly steady conditions of the engine, yet another control means is effective to prevent communication of the vacuum signal during wide-open throttle conditions of the engine carburetor.

United States Patent 1191 1111 3,835,827 Wolgemuth Sept. 17, 1974EXHAUST AND GAS RECIRCULATING Primary ExaminerWendell E. Burns SYSTEMAttorney, Agent, or FirmJoseph W. Malleck; Keith [75] Inventor: James H.Wolgemuth, Warren, Zerschlmg Mich. [73] Assigneer Ford Motor Company,Dearborn, [57] ABSTRACT Mich. An exhaust gas recirculation system isdisclosed employing a primary control valve having a vacuum oper- [22]Ffled' 1973 ated servo mechanism for controlling the admission of [21Appl. No.: 327,280 recirculating gases. The servo mechanism is operatedin response to a modulated vacuum signal derived [52] U S Cl 123/119 Aprincipally from intake manifold vacuum. Modulation [51] hhbl "F02!"25/06 of the vacuum Signal is achieved y three control [58] Fie'ld123/119 A means connected in series, one of which functions in responseto a differential between carbureted venturi [56] References Citedvacuum and the intake manifold vacuum, another control means operates toprevent communication of UNITED STATES PATENTS the vacuum signal to theservo mechanism during pro- 3,739,797 6/1973 Caldwell l23/1l9 A longedsteady or nearly steady Conditions Of the en- FOREIGN PATENTS ORAPPLICATIONS gine, yet another COl'ltl'Ol means is effective to prevent1 601 374 4 1970 Germany 123 119 A Commumcatlo of the vacuum sgnal durmgopen throttle conditions of the engine carburetor.

7 Claims, 1 Drawing Figure I 7/ i; //4 j EXHAUST AND GAS RECIRCULATINGSYSTEM BACKGROUND OF THE INVENTION Numerous systems have been devised torecycle exhaust gases into the air/fuel induction system of anautomotive engine for a variety of purposes among which include:

a. use of the exhaust gases to prewarm and thereby vaporize the incomingair/fuel mixture to facilitate its complete combustion in the combustionzone,

b. recirculation of the exhaust gases to reuse unignited or partiallyburned portions of the fuel which would otherwise pass out into theexhaust pipe and into the atmosphere, and

. recirculate exhaust gases for the purpose of reducing oxides ofnitrogen emitted from the exhaust system and into the atmosphere. Thisis brought about by reducing the maximum combustion temperature inconsequence of the dilution of the air/fuel mixture by the recycling ofexhaust gases.

However, since the load and power demands of the engine change ratherconsiderably over their normal operation, the above goals cannot beeasily achieved if consideration is given to driveability andsatisfactory engine performance. To this end, the invention is concernedwith utilizing control signals which vary the volume and timing ofexhaust gas recirculated in conformity with achieving more goals. It isknown that the recycling of at least 5 percent and not more than percentof the total exhaust gases through the engines, depending upon the loador power demand, will reduce the combustion temperature to less than2,200F. But within this range, the amount recycled at any one momentmust be tuned to a variety of engine conditions.

SUMMARY OF THE INVENTION The primary object of this invention is toprovide an exhaust gas recirculation system capable of introducingexhaust gases to the intake manifold system during periods when exhaustgas recirculation will not substantially hinder the normal poweroperation of the engine and in such modulated quantities that best suitthe attainment of lower emissions. To this end, the inventioncontemplates the control or admission of exhaust gas recirculation inresponse to a vacuum signal, the signal being modulated primarily inproportion to carburetor venturi vacuum. On and off controls areadditionally superimposed over this primary modulation by use of (a) avalve adapted to close on a delayed basis in response to a change inintake manifold vacuum and to remain closed during steady state manifoldvacuum conditions, and (b) a valve is adapted to close when wide-openthrottle conditions are substantially reached.

One or more combinations of the above controls provide a sensitivevariation of exhaust gas recirculation more in tune with the multipleneeds of the engine for top performance as well as the emissionscriteria.

To provide a constant relationship between recirculation and carburetedair flow, an admitting valve may be contoured to provide a flow areathrough the throat of the admitting valve which is proportional to theone half power of the modulated vacuum signal; the modulated vacuumsignal in turn may be related to venturi vacuum which increases at arate equal to the second power of the air-flow through the carburetor.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE is a schematic illustrationof the exhaust gas recirculation system used in conjunction with atypical internal combustion engine.

DETAILED DESCRIPTION Referring now to FIG. 1, a preferred embodiment isillustrated comprising, broadly, an exhaust gas recirculation systemadapted to operate with a typical engine having an intake system A andan exhaust manifold B, the intake system further comprising a carburetorhaving a typical air horn 9 provided with a metering venturi 10 forinducting fuel (not shown) in response to the vacuum created by saidmetering venturi. A throttle 8 is employed to conventionally control theflow of the fuel and air mixture passing into intake manifold 11 of theengine.

Exhaust gas recirculation is conveyed by a duct or passages Cinterconnecting the exhaust manifold with the intake manifold; primaryvalve means D is effective to control the admission of exhaust gasesthrough said duct C. Valve means D is operated in response to a servomechanism E which has a control element or diaphragm 23 normally biasedin one direction to close valve means D and is subject to a modulatedvacuum signal to overcome the effect of said bias for opening said valvemeans. Modulation of said vacuum signal is achieved through a series ofcontrol means H, G and F. Means H is effective to control thecommunication of intake manifold vacuum with the servo mechanism inresponse to a differential between intake system vacuum obtained at themetering venturi l0 and intake manifold vacuum. Control means F iseffective to interrupt normal communication of the modulated vacuumsignal to said servo mechanism in response to wideopen throttleconditions of said carburetor. Means G is effective to preventcommunication of the modulated vacuum signal with said servo mechanismduring prolonged steady state cruising conditions of the engine.

Turning now in more particularity to the components of the system,primary valve means D comprises a rigid valve housing 7 having acylindrical bore or wall 17 subdivided therein longitudinally intochamber portions 18, 19, 26 and 27 by the respective interposition offlat walls 16, 22 and a diaphragm 23 (forming a control element), allextending transversely across the bore at spaced locations. The wall 16has an opening 15 therein defining a valve seat; a valve element 14 ismovable between opened and closed positions (shown in the semi-openposition in FIG. 1) for said valve seat. The valve element 14 is carriedby a valve stem 25 connected with said flexible diaphragm 23 formovement therewith. Inlet 21 chamber portion 18 provides for introducingexhaust gases via conduit 12 from said exhaust manifold; outlet 20 fromchamber portion 19 is provided for communicating with the intakemanifold 11 of said intake system by way of a conduit 13 connecting witha port 92 positioned below the carburetor throttle 8.

The servo-mechanism E utilizes a helical spring 24 to bias diaphragm 23in a direction to bring valve element 14 to a closed position; spring 24acts between the right hand side of wall 22 and the left hand side ofdiaphragm 23. A passage 29 is provided to communicate chamber portion 26with the control vacuum signal conveyed from means F, G and H, means Hcommunicating directly with the port 91 of the intake manifoldimmediately below the throttle of the carburetor. The opposite side ofthe diaphragm 23 is subjected to pressure in chamber portion 27 which isvented V to atmosphere by way of passage 28.

Control means H, as indicated, is adapted to provide modulation ofintake manifold vacuum in accordance with a signal that rises and fallsmore closely with the conditions at which the engine can assimulateexhaust gas recirculation. For this purpose the vacuum generated at theprimary venturi of the carburetor is utilized; this signal is generallyproportional to the second power of the air-flow rate through the airhorn 9. When intake manifold vacuum will be generally high at low speedsof the engine, venturi vacuum will not be low; similarly at high enginespeeds, intake manifold vacuum will be generally insignificant whereasventuri vacuum will be available. To employ the venturi vacuum signal,control means H has a housing 6 defining a valve chamber 73 havingstepped cylindrical walls 73a, 73b and 73d; walls 73b and 73d areconnected by a tapered wall 730. A spool valve 74 is slidable in chamber73 and has cylindrical land 77 (having diameter 78) slidable in intimatecontact with the cylindrical wall 73a; land 75 (having diameter 79) isslidable in intimate contact with cylindrical wall 73b and diaphragm 86is connected at the juncture of tapered wall 730 and wall 73d to definechamber portions 84 and 85. The lands 77 and 75 are spaced apart, bystem 76, a distance so that in the position as viewed in FIG. 1, inlet95 and outlet 81 to chamber portion 80 are in communication.

Chamber portion 80 is defined by the lands 77 and 75; inlet 82 isconnected to a reservoir 98 by passage 95, the reservoir in turn is incommunication with intake manifold vacuum by way of conduit 65 leadingto port 91. To insure sufficient vacuum for system operation at lowintake manifold vacuum levels, an accumulator (in the form of reservoir98) is utilized; a check valve 100 acting against seat 101 is employedto preserve the reservoir vacuum. Outlet 81 is ultimately incommunication with the servo-mechanism E.

Chamber portion 85 (defined between the land 75 and the diaphragm 86) isin communication with atmosphere, identified as vent V, by way ofpassage 94. Chamber portion 84 (defined between the diaphragm 86 and theend of the chamber) has an inlet 88 in communication (by way of passage89) with a port 90 entering into the venturi of the carburetor.

To obtain modulation of the vacuum signal passing through means H, adifferential between intake manifold vacuum (acting on the innersurfaces of the spool valve) and venturi vacuum (acting on diaphragm 86)is employed. Initially, venturi vacuum from passage 89 will flex thediaphragm 86 to the right allowing the spool valve 74 to uncover inlet82, thereby admitting the intake manifold vacuum to the chamber portion80. Intake manifold vacuum operating against the differential faces oflands 77 and 75 will have a resultant force urging the spool valve tothe left and closing inlet 82. Thus, the resultant intake manifoldvacuum force will oppose that of the venturi vacuum operating on thediaphragm; the land areas are chosen so that the forces will begenerally in equilibrium or nearly so at midrange speed conditions forthe engine. If engine conditions are such that the venturi vacuum willpredominate over the intake manifold vacuum resultant, the spool valvewill move further to the right, admitting a larger degree of intakemanifold vacuum as the vacuum control signal. This may occur at higherspeed conditions. Should the intake manifold vacuum differentialpredominate, such as at low speeds or idle, the opposite will occur andthe valve 74 will be moved to restrict the inlet 82. When the spool 74is moved sufiiciently to substantially restrict or close the inlet 82,the vent V will be opened communicating with atmosphere by passage 96.The vent V cannot be uncovered by over movement of the spool valve tothe left because of its attachment to the diaphragm; this prevents aleak to manifold vacuum. All vents, in the various control means, aswell as in the primary valve means, are vented to the clean side of theengine air cleaner which is very-slightly below atmospheric pressure.

The modulation by means 1-! provides a type of amplification of a weaksignal (venturi vacuum) to a relatively strong signal (intake manifoldvacuum). At times it may be desirable to construct the apparatus toproduce a constant relationship between exhaust gas recirculation andthe carbureted air flow through the venturi 10. To accomplish thelatter, intake manifold vacuum in chamber portion (which is our controlvacuum) will be modulated further by intake manifold in chamber portion5 (this manifold vacuum, under most conditions will be slightlydifferent from the control vacuum in chamber 80). To this end, a passage97 communicates chamber portion 5 with port 91 of the carburetor. Thusat high manifold vacuum levels, the modulated control vacuumcommunicated to outlet 81 is reduced from the value which it wouldnormally have at low manifold vacuum levels. This offsets the effect ofthe vacuum signal on the differential pressure across the primary valveD (namely, the pressure at inlet 21 minus the pressure at the outlet20). Thus with high manifold vacuum, control vacuum will be somewhatlowered and the primary valve means D will not be open as far, therebyproviding a smaller flow area to compensate for the higher vacuum atinlet 21.

Proceeding directly to the third control means G (skipping for themoment the second control means F) further modulation of the controlvacuum signal is obtained in accordance with transient conditions of theengine. That is to say, the control vacuum will be admitted to permitexhaust gas recirculation during accelerations and short cruises when itis mot desirable to do so. Control means G comprises a housing 4defining a valve chamber having stepped portions; a first cylindricalwall 47 (having a diameter 44) is interrupted by a smaller cylindricalwall 48 (having a diameter 45). An enlarged chamber 56 is defined at theright hand side of the chamber. A spool valve 41 with three lands 42, 43and 53 is arranged to slidably reciprocate within the chamber portions;land 42 is adapted to slide in intimate relationship with thecylindrical wall 47, land 43 slides in intimate relationship withcylindrical wall 48, and the third land 53 (having a diameter similar toland 42) slides in intimate relationship with the right hand sideof thecylindrical wall 47. The spacing between lands 42 and 43 is arranged toprovide a chamber portion 3 and fluid communication between inlet 49 andoutlet 50 when the lands are so positioned as in FIG. 1.

A compression spring 55 is positioned between the v hand surface of land53; spring 55 urges spool valve 41 in a leftward direction causing theedge of the land 43 to move across the edge 82 of inlet 49 and therebyclose communication with the outlet. Similarly, the land 42 will uncovera vent allowing the space between the lands to be reduced tosubstantially atmospheric pressure. Chamber portions 58 and 56 (whichare on opposite sides of land 53) are interconnected by parallelpassages 62 and 63, both of which are commonly in communication withintake manifold vacuum via passage 66 and 65. Parallel passage 62contains a check valve adapted to allow intake manifold vacuum to enterchamber portion 56; the ball element 60 of the check valve will bemaintained away from valve seat 61 as the result of vacuum pressure.Parallel passage 63 contains a restriction 64 which acts as a delaymechanism in allowing the transient change in pressure between oppositesides of the restriction.

When intake manifold vacuum is constant, the communication to chamberportions 58 and 56 will impose equal forces on opposite sides of land53; spring 55 can thus cause the valve 41 to substantially close. Whenintake manifold vacuum increases due to deceleration, both the chamberportion 56 and the chamber portion 58 will be further evacuated quickly(check valve 60 will be open) and the valve 41 will still continue toremain substantially closed. However, when manifold vacuum decreases dueto an increase in engine acceleration, the check valve 60 will preventflow from chamber portion 56 through passage 62. The higher pressure inchamber portion 58 will force the spool valve to the right uncoveringthe inlet 49. The spool valve will move slowly due to the restriction 64with dampens fluid flow to or from chamber portion 56. When transientcondition has expired, the valve 41 will be urged by spring 55 to theleft to substantially close the inlet 49 and obtain equilibrium again.The time required to close the inlet 49 can be varied by changing thesize of the chambers portions 58 and 56 or changing the size of therestrictor 64.

Another damper or delay mechanism can be built in at the left hand sideof the valve means G by use of a vent passage 68 communicating withchamber portion 57. A parallel passage 67 is incorporated to alsocommunicate chamber portion 57 with the vent V. In pas sage 67, a oneway check valve is used, having a ball 70 adapted to seal against seat71 when vacuum pressure is sufficiently low in chamber portion 57. Arestrictor 69 is incorporated in passage 68 so as to delay flowtherethrough. Thus, the time required to close inlet 49 can beadditionally extended; when there is a transient change of conditionsurging the spool valve 41 to the right or left, the restrictors 69 and64, and ball check valves 70 and 60 will cooperate.

The control vacuum signal delivered from the means G intended for theservo-mechanism E can be further controlled by second control means F.Means F is adapted to prevent the admission of the control vacuum signalduring wide-open throttle conditions when exhaust gas recirculation isnot desired. Means F comprises a housing 2 defining a chamber 30 withinwhich is slidable a spool valve 31 having lands 32 and 33 spaced apartsufficiently to allow communication between an inlet 34 and an outlet 51for conducting the control vacuum signal. Valve 31 is normally urged toa closed position over inlet 34 by spring 35 residing in chamber portion40 defined between the right hand land 33 and the end of the chamber.The chamber portion 40 is normally in communication with intake manifoldvacuum by way of passage 36; the chamber portion 37 on the opposite sideof the spool valve (between land 32 and the end of the chamber) is incommunication with atmosphere by either passage 38 or 39 connected as avent V. Inlet 34 will be closed by the edge 52 of land 33 when manifoldvacuum decreases to such a level that the compression spring acting onthe spool valve, moves it sufficiently leftward. In the closed position,one of the vents will be open, particularly through passage 38. Thecontrol vacuum signal acting on the surfaces 32a and 33a of therespective lands 32 and 33 will offer no differential force urging thespool valve in either direction; therefore the differential between theforce of spring 35 and the force of intake manifold vacuum, conveyed bypassages 36 and 65, will determine the position of the spool valve 31.

The scope of this invention comprehends variations of the series ofcontrol means. For example, the system can be used without the transientvalve means G if exhaust gas recirculation is desired at steady statecruising conditions. Control means F could be eliminated in conjunctionwith reservoir 98; valve means D can then be recalibrated to provide ashut-off at the highest vacuum encountered at wide-open throttleconditions with metering of the recirculation over a small range whenabove the highest vacuum encountered.

I claim:

1. In an engine having an exhaust manifold, an intake system forinducting air and fuel through a metering venturi into an intakemanifold of said engine, an apparatus for recirculating exhaust gasescomprising:

a. a duct connecting said intake system and exhaust manifold,

b. valve means interposed in said duct having a first control elementnormally biased to a closed position and a servo mechanism operable toovercome said bias for variably opening said valve means, said servomechanism being connected to vacuum from said intake system, and

c. first control means to modulate. the connection of vacuum betweensaid intake system and servo mechanism in accordance with pressure atsaid metering venturi, said first control means being movable inresponse to a differential pressure between intake manifold vacuum andventuri vacuum to modulate and limit the degree of intake system vacuumcommunicated to said servo mechanism, said first control meanscomprising a housing having a bore with stepped portions, a spool valveprovided with differential lands slidable in respectively steppedportions of said bore, said bore having an inlet opening incommunication with said servo mechanism and an outlet opening incommunication with intake manifold vacuum, said outlet opening beingarranged so as to be opened or closed by operable movement of said spoolvalve, the larger of said lands being subject to a force on one sidethereof proportional to intake system airflow vacuum tending to movesaid spool valve to an open position about said outlet opening and theother side of said larger land being subject to the intake manifoldvacuum tending to urge said spool valve to a close position.

2. The apparatus as in claim 1, in which an accumulator is employed tomaintain a predetermined level of intake manifold vacuum forintroduction to said first control means during all conditions ofoperation except when said first control means is closed.

3. The apparatus as in claim 1, in which the smaller land is subjectedto intake manifold vacuum urging said first control means to an openposition and thereby maintaining a constant relationship between exhaustgas recirculation and intake system air-flow vacuum even during theclosed position of said spool valve.

4. The apparatus as in claim 1, comprising in combination a thirdcontrol means effective to prevent communication of said intake manifoldvacuum with said servo mechanism during prolonged steady state cruisingconditions of said engine.

5. The apparatus as in claim I, in which said bias for said servomechanism is calibrated to provide closure of said valve means at thehighest vacuum encountered at wide-open throttle for said engine andsaid bias being adapted to meter a small amount of exhaust gasrecirculation during throttle positions substantially adjacent towide-open throttle.

6. The apparatus as in claim 1, in which there is further providedadditional control means for controlling the communication of manifoldintake vacuum to said servo mechanism, said additional control meansbeing adapted to prevent communication of intake manifold vacuum to saidservo mechanism during steady-state conditions of said carburetor airflow.

7. The apparatus as in claim 6, in which said additional control meanscomprises a housing having a bore with an inlet thereto in communicationwith said servo mechanism and an outlet thereof in communication withthe inlet to said first control means, a valve elev

1. In an engine having an exhaust manifold, an intake system forinducting air and fuel through a metering venturi into an intakemanifold of saId engine, an apparatus for recirculating exhaust gasescomprising: a. a duct connecting said intake system and exhaustmanifold, b. valve means interposed in said duct having a first controlelement normally biased to a closed position and a servo mechanismoperable to overcome said bias for variably opening said valve means,said servo mechanism being connected to vacuum from said intake system,and c. first control means to modulate the connection of vacuum betweensaid intake system and servo mechanism in accordance with pressure atsaid metering venturi, said first control means being movable inresponse to a differential pressure between intake manifold vacuum andventuri vacuum to modulate and limit the degree of intake system vacuumcommunicated to said servo mechanism, said first control meanscomprising a housing having a bore with stepped portions, a spool valveprovided with differential lands slidable in respectively steppedportions of said bore, said bore having an inlet opening incommunication with said servo mechanism and an outlet opening incommunication with intake manifold vacuum, said outlet opening beingarranged so as to be opened or closed by operable movement of said spoolvalve, the larger of said lands being subject to a force on one sidethereof proportional to intake system air-flow vacuum tending to movesaid spool valve to an open position about said outlet opening and theother side of said larger land being subject to the intake manifoldvacuum tending to urge said spool valve to a close position.
 2. Theapparatus as in claim 1, in which an accumulator is employed to maintaina predetermined level of intake manifold vacuum for introduction to saidfirst control means during all conditions of operation except when saidfirst control means is closed.
 3. The apparatus as in claim 1, in whichthe smaller land is subjected to intake manifold vacuum urging saidfirst control means to an open position and thereby maintaining aconstant relationship between exhaust gas recirculation and intakesystem air-flow vacuum even during the closed position of said spoolvalve.
 4. The apparatus as in claim 1, comprising in combination a thirdcontrol means effective to prevent communication of said intake manifoldvacuum with said servo mechanism during prolonged steady state cruisingconditions of said engine.
 5. The apparatus as in claim 1, in which saidbias for said servo mechanism is calibrated to provide closure of saidvalve means at the highest vacuum encountered at wide-open throttle forsaid engine and said bias being adapted to meter a small amount ofexhaust gas recirculation during throttle positions substantiallyadjacent to wide-open throttle.
 6. The apparatus as in claim 1, in whichthere is further provided additional control means for controlling thecommunication of manifold intake vacuum to said servo mechanism, saidadditional control means being adapted to prevent communication ofintake manifold vacuum to said servo mechanism during steady-stateconditions of said carburetor air flow.
 7. The apparatus as in claim 6,in which said additional control means comprises a housing having a borewith an inlet thereto in communication with said servo mechanism and anoutlet thereof in communication with the inlet to said first controlmeans, a valve element therein normally biased in a closed positionpreventing flow between said inlet and outlet and a land connecting withsaid element having opposite sides thereof normally subjected to intakemanifold vacuum, and means for delaying the relief of intake manifoldvacuum from either side of said land upon a change of intake manifoldvacuum so that one side of said land will be effective to overcome saidbias and open said second control means according to said predetermineddelay.